Magnetoresistive memory device and manufacturing method of the same

ABSTRACT

According to one embodiment, a magnetoresistive memory device includes a first magnetic layer, a second magnetic layer on one major surface side of the first magnetic layer via a first nonmagnetic layer, a third magnetic layer on the second magnetic layer via a first Ru layer, a sidewall insulating film on sides of the layers, a fourth magnetic layer on an other major surface side of the first magnetic layer via a second nonmagnetic layer, and a fifth magnetic layer on the fourth magnetic layer via a second Ru layer. The reversed magnetic field of the second magnetic layer is smaller than that of the third and fourth magnetic layers, and the reversed magnetic field of the fifth magnetic layer is smaller than that of the third and fourth magnetic layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U. S. Provisional Application No.62/308,128, filed Mar. 14, 2016, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetoresistivememory device and a manufacturing method thereof.

BACKGROUND

In recent years, a large-capacity magnetoresistive random access memory(MRAM) using a magnetic tunnel junction (MTJ) element has been expectedand attracting attention. An MTJ element includes a tunnel barrier layerand two magnetic layers sandwiching the tunnel barrier layer, one of thetwo magnetic layers being a magnetization fixed layer (reference layer)in which the magnetization is fixed so that the direction ofmagnetization does not change, the other being a magnetization freelayer (storage layer) which the direction of magnetization may be easilyreversed. Further, in some cases, a shift cancelling layer is providedto suppress the influence of fringing field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view schematically showing a magnetoresistive memorydevice according to the first embodiment.

FIG. 2 is a sectional view taken along the line I-I′ of FIG. 1.

FIG. 3 is a sectional view taken along the line II-II′ of FIG. 1.

FIG. 4 is a sectional view showing the structure of a memory cellportion of the magnetoresistive memory device according to the firstembodiment.

FIGS. 5A to 5C are schematic diagrams showing a method of setting themagnetization of a reference layer and a shift cancelling layer.

FIG. 6 is a schematic diagram showing how the magnetic field of themagnetic layer is reversed by application of an external magnetic field.

FIGS. 7A to 7C are schematic diagrams showing a method of setting themagnetization of a reference layer and a shift cancelling layer.

FIGS. 8A to 8C are schematic diagram: showing a method of setting themagnetization of a reference layer and a shift cancelling layer.

FIGS. 9A to 9C are schematic diagrams showing a method of setting themagnetization of a reference layer and a shift cancelling layer.

FIG. 10 is a sectional view showing the structure of a memory cellportion of a magnetoresistive memory device according to the secondembodiment.

FIGS. 11A to 11E are sectional views showing a manufacturing process ofthe memory cell portion of FIG. 10.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetoresistive memorydevice comprises: a first magnetic layer; a second magnetic layerprovided on one major surface side of the first magnetic layer via afirst nonmagnetic layer; a third magnetic layer provided on the secondmagnetic layer, which is opposite to the first magnetic layer via afirst Ru layer; a sidewall insulating film provided on the sides of thefirst to third magnetic layers; a fourth magnetic layer provided on another major surface side of the first magnetic layer via a secondnonmagnetic layer; and a fifth magnetic layer provided on the fourthmagnetic layer, which is opposite to the first magnetic layer via asecond Ru layer. The reversed magnetic field of the second magneticlayer is smaller than that of the third and fourth magnetic layers, andthe reversed magnetic field of the fifth magnetic layer is smaller thanthat of the third and fourth magnetic layers.

First Embodiment

FIG. 1 is a plan view schematically showing the magnetoresistive memorydevice according to the first embodiment. FIG. 2 is a sectional viewtaken along the line I-I′ of FIG. 1 and FIG. 3 is a sectional view takenalong the line II-II′ of FIG. 1. The members illustrated by dashed linesin FIGS. 2 and. 3 show plugs SC in a back side, which are not seen inthe I-I′ section or section.

The magnetoresistive memory device of this embodiment is an MRAMcomprising an MTJ element (magneto-resistive effect element) of a spintransfer torque write type as a storage device. A perpendicularmagnetization film is employed as the MTJ element. The perpendicularmagnetization film is a magnetization film in which the direction ofmagnetization (direction of axis of easy magnetization) is substantiallyperpendicular to the surface of the perpendicular magnetization film.

In the drawings, 101 indicates a silicon substrate (a semiconductorsubstrate), and an element isolation region 102 is formed on a surfaceof the silicon substrate 101. The element isolation region 102 definesan active region.

The MRAM of this embodiment comprises a first select transistor whosegate electrode is a word line WL1, a first MTJ element F connected toone of source-drain areas 104 (that is, drain area D1) of the firstselect transistor, a second select transistor whose gate electrode is aword line WL2, and a second MTJ element M connected to one of thesource-drain areas 104 (that is, drain area D2) of the second selecttransistor. The figures also illustrate a protective insulation film103. That is, one memory cell of this embodiment comprises oneMTJ(storage device) and one select transistor, and two selecttransistors of adjacent memory cells share the source-drain areas 104 ofthe other side (source regions S1 and S2).

The gate (gate insulating film and gate electrode) of the selecttransistor of this embodiment is embedded in the surface of the siliconsubstrate 101. In other words, the gate of the select transistor has aburied gate (BC) structure. Similarly, the gate for element isolation(that is, word line I-WL) also has a BG structure.

The source-drain area 104 (D1) of the first select transistor isconnected to the bottom of the first MTJ element M via a bottomelectrode BEC. The top of the first MTJ element M is connected to a bitline BL2 via a top electrode TEC. The other source-drain area 104 (S1)of the first select transistor is connected to a bit line BL1 via a plugSC.

In this embodiment, the planer patterns of the bottom electrode BEC, MTJelement M, top electrode TEC and plug SC are circular, but they may beother shapes.

The source-drain area 104 (D2) of the second select transistor isconnected to the bottom of the second MTJ element M via the bottomelectrode BEC. The top of the second MTJ element M is connected to a bitline BL2 via the top electrode TEC. The other source-drain area 104 (S2)of the second select transistor is connected to the bit line BL1 via theplug SC.

The first select transistor, the first MTJ element M, the second selecttransistor and the second MTJ element M (two memory cells) are providedfor each active area. Two adjacent active areas are separated by theelement isolation area 102.

Word lines WL3 and WL4 correspond to the word lines WL1 and WL2,respectively. Therefore, the first select transistor whose word line WL3is a gate, the first MTJ element M connected to one source-drain area ofthe first select transistor, the second select transistor whose wordline WL4 is a gate and the second MTJ element M connected to onesource-drain area of the second select transistor constitute two memorycells.

Note that the layout of the MTJ elements, BL, WL, etc. is not limited tothat shown in FIGS. 1 to 3. For example, as shown in patent literature 1(US 2014/0284738 A1), BL1 may be provided in a layer lower than that ofBL2 in the structure. Furthermore, as shown in patent literature 2 (U.S.Pat. No. 8,513,751 B-2), the active area may he inclined with respect tothe gate electrode in the structure.

FIG. 4 is a sectional view showing a concrete structure of the MTJelement part used for this embodiment.

A first reference layer (a second magnetic layer [RL-1]) 22 is formed ona major surface (upper surface) side of a storage layer (first magneticlayer [SL]) 10 to store data via a tunnel barrier layer (firstnonmagnetic layer) 21. A first shift cancelling layer (a third magneticlayer [SCL-1]) 24 is formed on a surface of the first reference layer22, which is opposite to the storage layer 10 via a first Ru layer 23. Asecond reference layer (a fourth magnetic layer [RL-2]) 32 is formed onthe other main surface (lower surface) side of the storage layer 10 viaa tunnel barrier layer (second nonmagnetic layer) 31. A second shiftcancelling layer (fifth magnetic layer [SCL-2]) 34 is formed on asurface of the second reference layer 32, which is opposite to thestorage layer 10 via a second Ru layer 33.

As described above, this embodiment employs the structure of a dualjunction MTJ element, which includes the reference layers 22 and 32 arearranged on both sides of the storage layer 10 in order to improve thewrite efficiency in the storage layer 10.

Note that these layers 10 to 34 are formed between the bottom electrode(BEC) and the top electrode (TEC). In other words, the second shiftcancelling layer 34 is formed on the bottom electrode (BEC) and thelayers 10 to 34 are processed into the pattern of the MTJ element (forexample, circular). Further, the top electrode (TEC) is connected to thefist shift cancelling layer 24.

The storage layer 10 is of CoFeB, for example, and has magneticanisotropy perpendicular to the film surface, with variable themagnetization direction. The material of the storage layer 10 is notlimited to CoFeB, but various kinds of magnetic substances can beemployed.

The tunnel barrier layers 21 and 31 are layers in which tunnel currentis allowed to flow, and various kinds of nonmagnetic substances can beemployed therefor. In this embodiment, for example, the tunnel barrierlayer 21 is of Cu or MgO and the tunnel barrier layer 31 is of MgO.Moreover, the tunnel barrier layer 31 is thinner than the tunnel barrierlayer 21. It suffices if the tunnel barrier layers 21 and 31 are ofnonmagnetic layers, for which an oxide containing not only Cu or MgO butSi, Ba, Ca, La, Mn, Zn, Hf, Ta, Ti, B, Cr, V, or Al may be used.

The reference layers 22 and 32 consist of CoFeB, for example, and havemagnetic anisotropy perpendicular to the film surface, with fixedmagnetization direction. The material of the reference layers 22 and 32is not limited to CoFeB, but various kinds of magnetic substances can beemployed. For example, it is possible to use Fe/Pt (artificial latticestructure by a lamination structure of Fe and Pt), Fe/Pd, Co/Pt, Co/Pd,CoCrPt or CoCrPd. The reference layers 22 and 32 have magnetizationdirections reverse to each other.

The shift cancelling layers 24 and 34 are of Fe/Pt, for example, andnave magnetic anisotropy perpendicular to the film surface, with thefixed magnetization direction. The material of the shift cancellinglayers 24 and 34 is not limited to Fe/Pt, but various kinds of magneticsubstances can be employed as in the case of the reference layers 22 and32. In this embodiment, for example, the reference layer 32 and theshift cancelling layer 24 may be of Fe/Pt, Fe/Pd, CoCrPt or CoCrPd andthe reference layer 22 and the shift cancelling layer 34 may be of Co/Ptand Co/Pd.

Note that the magnetization direction of the first shift cancellinglayer 24 is opposite to that of the first reference layer 22 and themagnetization direction of the second shift cancelling layer 34 isopposite to that of the second reference layer 32.

The Ru layers 23 and 33 may be of some other metal material as long asthey are suitable for making the upper and lower magnetic layers to beanti-parallel to each other. The thickness of the Ru layers 23 and 33 issufficiently thin as compared to the reference layers 22 and 32, theshift cancelling layers 24 and 34 or the like, and it is, for example, 3to 7 nm.

The reference layer 22, Ru layer 23 and shift cancelling layer 24 form asynthetic anti-ferromagnetic (SAP) structure 20 in which two magneticlayers are anti-ferromagnetically exchange-coupled. Similarly, thereference layer 32, Ru layer 33 and shift cancelling layer 34 also forman SAP structure 30. Thus, the magnetoresistive memory device of thisembodiment comprises a dual junction MTJ element which employs the SAFstructure.

The storage layer 10, tunnel barrier layer 21, reference layer 22, Rulayer 23 and shift cancelling layer 24 have widths or diameters lessthan those of the tunnel barrier layer 31, reference layer 32, Ru layer33 and shift cancelling layer 34, respectively. More specifically, thelayers 10, 21 to 24 and 31 to 34 are stacked one on another, and thenthe storage layer 10, tunnel barrier layer 21, reference layer 22, Rulayer 23 and shift cancelling layer 24 are etched into the pattern ofthe MTJ element. Further, the tunnel barrier layer 31, reference layer32, Ru layer 33 and shift cancelling layer 34 are etched into a patternslightly greater than the MTL element pattern.

A sidewall insulating film (side wall spacer) 40 of silicon nitride orthe like is provided on the side surfaces of the storage layer 10,tunnel barrier layer 21, reference layer 22, Ru layer 23 and shiftcancelling layer 24. This embodiment employs such a structure that astep is produced between an upper SAF structure 20 and a lower SAFstructure 30.

Note that thickness T2 (T_(RL1)) of the first. reference layer 22,thickness 13 (T_(SCL1)) of the first shift cancelling layer 24,thickness 14 (T_(RL2)) of the second reference layer 32 and thickness T5(T_(SCL2)) of the second shift cancelling layer 34 are such that:

T_(RL1)<T_(SCL2)<T_(RL2)<T_(SCL1)   (1)

Further, reversed magnetic field H_(RL1) of the first reference layer22, reversed magnetic field H_(SCL1) of the first shift cancelling layer24, reversed magnetic field H_(RL2) of the second reference layer 32 andreversed magnetic field H_(SCL2) of the second shift cancelling layer 34are such that:

H_(RL1)<H_(SCL2)<H_(RL2)<H_(SCL1)   (2).

This is because, if similar types of materials are used the magneticlayers, not only the intensity of the magnetic field becomesproportional to the thickness of the film, but also the magnitude of thereversed magnetic field is proportional to the thickness of the film.

Next, how to determine the magnetization of the magnetic layers 22, 34,32 and 34 of the magnetoresistive memory device of this embodiment willbe described.

First, the layers 34, 33, 32, 31, 10, 21, 22, 23, and 24 are formed inthis order on a bottom electrode (BEC). Here, the thicknesses of thefirst reference layer (RL-1) 22, first shift cancelling layer (SCL-1)24, second reference layer (RL-2) 32 and second shift cancelling layer(SCL-2) 34 are set according to the relationship (1).

Next, a mask material layer (not shown) of silicon. nitride is formed onthe shift cancelling layer 24, and then the shift cancelling layer 24,Ru layer 23, reference layer 22, tunnel barrier layer 21 and storagelayer 10 are selectively etched into an MTJ element pattern.Subsequently, an insulating sidewall film 40 of silicon nitride, forexample, is formed on the sides of the layers 24, 23, 22, 21 and 10exposed by the etching. After that, using the mask material layer andthe insulating sidewall film 40 as a mask, the tunnel barrier layer 31,reference layer 32, Ru layer 33 and shift cancelling layer 34 areselectively etched.

The resultant structure thus prepared is exposed to a first externalmagnetic field applied thereto perpendicular to the film surface, asshown in FIG. 5A, so as to uniform the magnetization directions of thereference layers 22 and 32 (RL-1, RL-2) and the shift cancelling layers24 and 34 (SCL1, SCL-2). Note that the magnetization directions of theselayers are uniformed here in the downward direction, but they may be alldirected upward.

Subsequently, as shown in FIG. 5B, a second external magnetic fieldweaker than the first external magnetic field and in a directionopposite to that of the first external magnetic field is applied to thestructure, and thus the magnetization direction of the first referencelayer (RL-1) 22, which is the thinnest film of the layers 22, 24, 32 and34, is reversed.

Further, as shown in FIG. 5C, a third external magnetic field strongerthan the second external magnetic field and in the same direction asthat of the second external magnetic field is applied to the structure,and thus the magnetization direction of the second shift cancellinglayer (SCL-2) 34, which is the second thinnest film, is reversed.

Note that arrows appearing on left-hand sides of FIGS. 5A to 5C show howthe external magnetic fields are applied. FIG. 5A illustrates that thedownward first external magnetic field is applied. FIG. 5B illustratesthat the downward first external magnetic field is applied and then anupward second external magnetic field weaker than the first externalmagnetic field is applied. FIG. 5C illustrates that an upward thirdlarger external magnetic field, which is stronger than the secondexternal magnetic field but weaker than the first external magneticfield is applied after applying the second external magnetic field.

FIG. 6 shows how the magnetic field of the magnetic layers is reversedduring the external magnetic field applied once to a (+) side is thengradually reduced from a maximum of the (+) side. The (+) sidecorresponds to a section below the arrow on the left-hand side of eachof FIGS. 5A to 5C, whereas an (−) side corresponds to a section abovethe arrow on the left-hand side of each of FIGS. 5A to 5C. If theexternal magnetic field is applied to the maximum on the (+) side, allof SCL-1, RL-1, SCL-2 and RL-2 are magnetized downward (FIG. 5A). Here,the order of the layers in the magnetization is arbitrary. Whiledecreasing the external magnetic field to the (−) side, RL-1 is reversedfirst (FIG. 5B) and then SCL-2 is reversed (FIG. 5C).

The reason that the magnetic fields of the first reference layer 22 andthe second shift cancelling layer 34 are reversed in the above-describedmanner is that as the thickness of the magnetic layer is less, themagnetization direction can be more easily reversed. Further, as shownin FIGS. 5B and 5C, the first, second and third external magnetic fieldsmay not be applied in this order, but it is possible to apply the thirdexternal magnetic field after the first external magnetic field.

Here, the stray magnetic field in the storage layer 10 is greatlyaffected by the magnetic field produced the edge of the reference layer.In this embodiment, the edge of the second reference layer 32, which hasa strong magnetic field, is apart from the edge of the storage layer 10.With this structure, the influence of the stray magnetic field fromreference layer 32 of the strong magnetic field can be reduced. Further,among the layers 22, 24, 32 and 34, the reference layer 22 has theweakest magnetic field, the influence of the stray magnetic field by theedge of the reference layer 22 also can be reduced. Thus, the straymagnetic field in the storage layer 10 can be reduced.

The method of setting the magnetic field is not necessarily limited tothat shown in FIGS. 5A to 5C, but it may be the method shown in FIGS. 7Ato 7C.

As shown in FIG. 7A, the thicknesses of the first reference layer (RL-1)22, the first shift cancelling layer (SCL-1) 24, the second referencelayer (RL-2) 32 and the second shift cancelling layer (SCL-2) 34 are setsuch that:

T_(SCL-2)<T_(RL-1)<T_(RL2)T_(SCL1)   (3).

In this state, the first external magnetic field is applied as in thecase shown in FIG. 5A.

Next, as shown in FIG. 7B, the second external magnetic field, which isweaker than the first external magnetic field and in the oppositedirection to that of the first external magnetic field is applied toreverse the magnetization direction of the second shift-cancelling layer(SCL-2) 34, which is the thinnest of the layers 22, 24, 32 and 34.

Further, as shown in FIG. 7C, the third external magnetic field strongerthan the second external magnetic field and in the same direction asthat of the second external magnetic field is applied to reverse themagnetization direction of the second thinnest first reference layer(RL-1) 22.

Also in this case, since the edge of the second reference layer 32having a strong magnetic field can be placed apart from the edge of thestorage layer 10, and therefore an effect similar to the case shown inFIGS. 5A to 5C is obtained. Note that the magnetic field of the firstreference layer 22 is weaker than that of the second reference layer 32or the first shift cancelling layer 24, but stronger than that of thesecond shift cancelling layer 34. As a result, the effect of the edge ofthe reference layer 22 becomes greater than the case shown in FIGS. 5Ato 5C. For this reason, as the method of determining the magnetic field,the method shown in FIGS. 5A to 5C is more desirable.

There are methods of setting a magnetic field such as shown in FIGS. 8Ato 8C and FIGS. 9A to 9C, but these methods are not desirable in thefollowing points.

That is, as shown in FIG. 8A, the thicknesses of the first referencelayer (RL-1) 22, the first shift cancelling layer (SCL-1) 24, the secondreference layer (RL-2) 32 and the second shift cancelling layer (SCL-2)34 are such that:

T_(RL2)<T_(RL-1)<T_(SCL-2)<T_(SCL1)   (4).

In this state, the first external magnetic field is applied as in thecase shown in FIG. 5A.

Next, as shown in FIG, 8B, the second external magnetic field, which isweaker than the first external magnetic field and in the oppositedirection to that of the first external magnetic field is applied toreverse the magnetization direction of the second reference layer (RL-2)32, which is the thinnest of the layers 22, 24, 32 and 34.

Further, as shown in FIG. 8C, the third external magnetic field strongerthan the second external magnetic field and in the same direction asthat of the second external magnetic field is applied to reverse themagnetization direction of the second thinnest first reference layer(RL-1) 22.

In the above-described case, the magnetization direction of thereference layers 22 and 32 becomes the same as that of the storage layer10. As a result, the advantageous effect of the dual function MTJelement, that is, the improvement of the write efficiency in the storagelayer 10 cannot be obtained.

As shown in FIG. 9A, the thicknesses of the first reference layer (RL-1)22, the first shift cancelling layer (SCL-1) 24, the second referencelayer (RL-2) 32 and the second shift cancelling layer (SCL-2) 34 are setsuch that:

T_(SCL1)<T_(RL2)<T_(RL1)<T_(SCL2)   (5).

In this state, the first external magnetic field is applied as in thecase shown in. FIG. 5A.

Next, as shown in FIG. 9B, the second external magnetic field, which isweaker than the first external magnetic field and in the oppositedirection to that of the first external magnetic field is applied toreverse the magnetization direction of the first shift cancelling layer(SCL-1) 24, which is the thinnest of the layers 22, 24, 32 and 34.

Further, as shown in FIG. 9C, the third external magnetic field strongerthan the second external magnetic field and in the same direction asthat of the second external magnetic field is applied to reverse themagnetization direction of the second thinnest second reference layer(RL-2) 32.

In the above-described case, the storage layer 10 will be stronglyaffected by the influence of the edge of the first reference layer 22,which has a larger magnetic field among the reference layers 22 and 32.In other words, the reference layer 22 having a strong magnetic field islocated close to the storage layer 10. As a result, the advantageouseffect which should be obtained by the sidewall spacer cannot beobtained.

As described above, according to this embodiment, the dual junction. MTJelement adopts an SAF structure and a sidewall spacer, with which thestrength of the magnetic field. (reversed magnetic field) of each of themagnetic layers 22, 24, 32 and 34 is optimized. In this manner, thelateral-direction stray magnetic field in the storage layer 10 can bereduced. This is because, with the adoption of the SAF structure, thereference layers 22 and 32 can be thinned, and with the adoption of theside wall spacer, the edge of the reference layer 32, which has a largemagnetic field, can he kept away from the storage layer 10. Thus, thewrite efficiency and the data retention characteristics in the MTJelement can be improved.

Here, in the dual junction MTJ element, the magnetization directions ofthe two reference layers 22 and 32 are opposite to each other, andtherefore the stray magnetic field in the lateral direction is large inthe storage layer 10. If the lateral-direction stray magnetic fieldbecomes large, the element characteristic (Ic/Δ), which is determined bythe write current Ic and the heat stability Δ are deteriorated. In otherwords, the object of improvement in the write efficiency becomesunachievable. On the other hand, in this embodiment, by adopting the SAFstructure and sidewall spacer described above, which produces adifference in reversed magnetic field, the influence of the straymagnetic field produced can he minimized, thereby making it possible toimprove the write efficiency and data retention characteristics.

Second Embodiment

Next, the structure of the memory cell portion including an MTJ elementand the manufacturing method therefor will be described in more detail.

FIG. 10 is a sectional view showing the structure of a memory cellportion of a magnetoresistive memory device according to the secondembodiment.

Switching MOS transistors are formed in a surface portion of an Sisubstrate 101, and an interlayer insulating film 121 is formed thereon.Each transistor has an embedded gate structure in which a gate electrode112 is embedded in a groove made in the substrate 101 via a gateinsulating film 111. The gate electrode 112 is embedded halfway in thegroove, and a protective insulation film 103 is formed thereon.Moreover, p- or n-type impurities are diffused in the substrate 101 onboth sides of the embedded gate structure, thereby forming asource-drain area, though not illustrated in the figure.

Note that the structure of the transistor is not limited to the typehaving an embedded gate structure. For example, such a structure may beadopted that a gate electrode is formed on the surface of the Sisubstrate 101 via a gate insulating film. The structure of thetransistor may be arbitrary as long as it can function as a switchingelement.

A contact hole formed in the interlayer insulating film 121 to beconnected to the drain of the transistor, and a bottom electrode (BEC)122 is embedded in the contact hole. The bottom electrode 122 is of sucha metal which has crystallinity, as TiN or W. The material of the bottomelectrode 122 is not limited to these, but may be arbitrary as long asit can be embedded well in a contact hole, and has sufficientconductivity.

On the bottom electrode 122, layers 10 to 34, which give rise to an MTJelement, are formed and further a sidewall insulating film 40 is formed.

An interlayer insulating film 123 is formed on the substrate on whichthe MTJ element and the sidewall insulating films 40 were formed. A topelectrode (contact plug: TEC) 124 connected to a first shift cancellinglayer 24 of the MT J element part is embedded in the interlayerinsulating film 123. Further, a contact plug 125 connected to the sourceor the transistor is embedded through the interlayer insulating film 123and the interlayer insulating film 121. Then, an interconnecting line(BL) 126 connected to the contact plug 124 and an interconnecting line(SL) 127 connected to the contact plug 125 are formed on the interlayerinsulating film 123.

Next, a method of preparing a memory cell portion of this embodimentwill he described with reference to FIGS. 11A to 11E.

First, as shown in FIG. 11A, a switching MOS transistor (not shown)having an embedded gate structure on a surface portion of the Sisubstrate 101 is formed, and then the interlayer insulating film 121 of,for example, SiO₂, is deposited on the Si substrate 101 by a CVD method.Subsequently, a contact hole is formed in the interlayer insulating film121, to be connected to the drain of the transistor, and then the bottomelectrode 122 of crystalline Ta is embedded in the contact hole. Morespecifically, a TiN film is deposited on the interlayer insulating film121 so as to berry the contact hole by a sputtering method or the like,and then the TiN film on the interlayer insulating film 121 is removedby chemical mechanical polishing (CMP), so that the TiN film remainsonly in the contact hole.

Next, as shown in FIG. 11B, on the interlayer insulating film 121 andthe bottom electrode 122, the layers 34, 33 and 32 for the SAP structure30, the second tunnel barrier layer 31, the storage layer 10, the firsttunnel barrier layer 21 and the layers 22, 23 and 24 for the SAPstructure 20 are formed by sputtering.

Note that before forming a magnetic material layer, a buffer layer 41may be formed by sputtering. The buffer layer 41 should desirably be ofa metal with. high electro-conductivity. Moreover, in order to suppressthe diffusion to the upper layer side of the MTJ element, anelectrically conductive oxide film or nitride film with may be employed.

Next, as shown in FIG. 110, a mask material layer 43 of an MTJ elementpattern is formed on the shift cancelling layer 24. Then, using the maskmaterial layer 43 as the mask, the shift cancelling layer 24 to thestorage layer 10 are selectively etched by an ion-beam. etching method.

Next, as shown in. FOG. 110, a sidewall insulating films 40 is formed onthe sides of the storage layer 10, tunnel barrier layer 21, referencelayer 22, Ru layer 23 and shift cancelling layer 24. The sidewallinsulating films 40 is formed in a self-aligned manner by depositing aninsulating film such as SiN on the entire surface, followed byetching-back by an RIE method or the like.

Next, as shown in FIG. 11E, using the mask material layer 43 and thesidewall insulating film 40 as the mask, the tunnel barrier layer 31 tothe buffer layer 41 are selectively etched by the ion-beam etchingmethod. Thus, the pattern of the MTJ element is obtained. Note that whenan insulating film, such as of SiN is used as the mask material layer43, the mask material layer 43 need to be removed after forming the MTJpattern. On the other hand, when a conductive material such as Ta or Ruis used as the mask material layer 43, the mask material layer 43 may beleft even after forming the pattern of the MTJ element.

Thereafter, the interlayer insulating film 123 of, for example, SiO₂, isformed, and then the contact plugs 124 and 125 and also theinterconnecting lines 126 and 127 are formed. Thus, the structure shownin FIG. 10 is obtained.

As described above, according to this embodiment, the memory cell of amagnetoresistive memory device can be prepared by forming the dualjunction MTJ element of SAF structure on a substrate including a selecttransistor. Further, the stray magnetic field in the storage layer 10can be reduced by forming the side wall spacer and optimizing theintensity of the in magnetic field (reversed magnetic field) of each ofthe magnetic layers 22, 24, 32 and 34. Therefore, the write efficiencyand data-retention characteristics in the MTJ element 10 can beimproved.

(Modification)

The embodiments are riot limited to those discussed above.

In the embodiments described above, the SAF structure is formed on bothsides of the storage layer, but a dual junction MTJ element having theSAF structure only on one side is also adoptable. In this case, the SAFstructure may be located below the storage layer or thereabove (that is,on the side where there is the sidewall insulating film). When locatedabove, it suffices if the magnetization directions of the firstreference layer (RL-1) and the second reference layer (RL-2) areopposite to each other, and the magnetic field of the first referencelayer is weaker than that of the second reference layer.

More specifically, when the second shift cancelling layer (SCL-2) isabsent:

T_(SCL1)>T_(RL1), T_(RL2)>T_(RL1)

H_(SCL1)>H_(RL1), H_(RL2)>H_(RL1)

or when the first shift cancelling layer (SCL-1) is absent:

T_(RL2)>T_(SCL2)>T_(RL1), H_(RL2)>H_(SCL2)>H_(RL1).

Further, the materials of the layers are not limited to those describedin the embodiments, but may be changed as needed according tospecification. Further, the thickness of each layer can also be suitablychanged according to specification.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit

1-6. (canceled)
 7. A magnetoresistive memory device comprising: a firstmagnetic layer; a second magnetic layer provided on one major surfaceside of the first magnetic layer via a first nonmagnetic layer; a thirdmagnetic layer provided on a surface side the second magnetic layerwhich is opposite from the first magnetic layer, via a first Ru layer; asidewall insulating film provided on sides of the first to thirdmagnetic layers; a fourth magnetic layer provided on an other anothermajor surface side of the first magnetic layer via a second nonmagneticlayer, a side surface of the fourth magnetic layer being located on anouter side with respect to a side surface of the first magnetic layer;and a fifth magnetic layer provided on a surface side of the fourthmagnetic layer which is opposite from the first magnetic layer, via asecond Ru layer; wherein: the second and fourth magnetic layers comprisea material of a same kind, and the third and fifth magnetic layerscomprise a material of a same kind, the second magnetic layer is thinnerthan the third and fourth magnetic layers, and the fifth magnetic layeris thinner than the third and fourth magnetic layers.
 8. The device ofclaim 7, wherein: the second and fifth magnetic layers have a samemagnetization direction, and the third and fourth magnetic layers havethe same magnetization direction, but opposite to the magnetizationdirections of the second and fifth magnetic layers.
 9. (canceled) 10.The device of claim 7, wherein: a reversed magnetic field of the secondmagnetic layer is smaller than that of the third and fourth magneticlayers, and a reversed magnetic field of the fifth magnetic layer issmaller than that of the third and fourth magnetic layers.
 11. Thedevice of claim 7, wherein: the first magnetic layer is a storage layerwhich stores data, the first and second nonmagnetic layers are barrierlayer layers into which tunnel current flows, the second and fourthmagnetic layers are reference layers having magnetic anisotropyperpendicular to a film surface, and the third and fifth magnetic layersare shift cancelling layers having magnetic anisotropy perpendicular toa film surface, which inhibit an influence of a stray magnetic field bythe reference layers.
 12. The device of claim 7, wherein each pair ofthe second and third magnetic layers and the fourth and fifth magneticlayers have an anti-ferromagnetic (synthetic anti-ferromagnetic [SAF])structure in which the two magnetic layers are anti-ferromagneticallyexchange-coupled.
 13. The device of claim 7, wherein: the third magneticlayer is thicker than the fourth magnetic layer, and the second magneticlayer is thinner than the fifth magnetic layer.
 14. The device of claim7, wherein: a reversed magnetic field of the third magnetic layer isstronger than that of the fourth magnetic layer, and a reversed magneticfield of the second magnetic layer is weaker than that of the fifthmagnetic layer.
 15. The device of claim 7, wherein magnetizationdirections of the second to fifth magnetic layers are perpendicular to asurface of each of the layers. 16-19. (canceled)